Waste Not, Want Not

As the 21st century begins, the concept of "waste" water is beginning to disappear. The reason is simple: We have no water to waste. Protecting water from pollution, and using it more sparingly, are the first steps in cutting waste.

But some cities and towns are going further--a lot further. They're taking something that was once a disposal problem--sewage--and re-imagining it as a solution to water shortage. Water experts call this carefully treated substance "reclaimed" water.

Cleansed by the Light

Ultraviolet light--invisible, short-wave radiation--damages DNA. That's why just exposing water to sunlight for a day can help kill microbes. In Singapore and other cities that are reclaiming water, experts take advantage of the power of UV light. Wastewater goes through a complex series of processes, including pumping it at high pressure through an ultrafine filter to exclude all but the tiniest particles, before hitting it with UV light as a final precaution.

As Dry as it Gets

Windhoek, the capital of Namibia, in southern Africa, is one of the driest places on Earth. To extend its shrinking water supply, the city has introduced reclaimed water to reservoirs since the late 1960s, sometimes at levels up to 30%, with no ill effects.